Species hotspots hard to pin down

Study finds little overlap between hotspots based on different types of biodiversity.

A global survey of birds has revealed how hard it can be to identify 'hotspots' of species diversity that need to be protected.

The mapped distribution of 9,500 bird species shows that there are major differences between hotspots based on three different types of biodiversity; it all depends on whether you refer to areas rich in species diversity in general, threatened species specifically, or endemic species, which have a limited habitat.

The new finding suggests that targeting hotspots for conservation using just one measure of biodiversity risks missing many species that deserve protection, says David Orme of Imperial College London, lead author of the study in Nature1.

Many previous studies have suggested that there is an overlap between, for example, threatened and endemic species, which makes intuitive sense. You might expect species to be endangered because of their limited range, Orme says.

Out of synch

But Orme and colleagues found this not to be true, at least for birds. "If you pick areas to conserve on the basis of where there are lots of endemic birds then this doesn't capture other types of diversity as well," Orme says. "In fact, it captures it surprisingly badly."

With many different definitions of 'hotspots' abounding, the team defined them as the top 2.5% of world locations sporting the highest diversity by each of their three criteria.

They then report that, for birds, threatened- and endemic-species hotspots share just 6.8% of their combined area. All three hotspot types share just 2.5% of their total area - and all of this overlap occurs in one area of the world: the Andes.

This will make it more difficult to define areas for conservation, says Pamela Rasmussen, an ornithologist at Michigan State University who is a coauthor of the study. "It is still possible, but it's not going to be easy," Rasmussen says.

Different factors affect different types of diversity, notes Orme. Mountain ranges such as the Andes tend to harbour the most species, because they contain many different climate zones. Islands harbour the most endemic species because they are isolated. And threatened species are most likely to be found close to areas where many humans live, such as on the Malaysian peninsula.

The road ahead

Some conservation groups argue that the new study won't necessarily affect their decision-making process about which areas to protect. For example, most threatened and endemic hotspots identified in the new study are already included in Conservation International's list of places that need protecting, notes Hugh Possingham, an ecologist at the University of Queensland in Brisbane, Australia. Conservation International is a non profit organization that bases its strategy on a different hotspot principle.

The best approach may be to look at all definitions of hotspots, say experts. "The different versions need not be viewed as competitive," says Norman Myers of Oxford University who invented the hotspot principle in 19882. "Rather, they should be considered to be mutually supportive."

Others say that instead of arguing over the definition of a hotspot, conservationists should simply use computer simulations to check which strategies best avoid species loss. "I think the way ahead is to 'road test' different approaches, not to continue demonstrating whether there is overlap between hotspots based on different measures of biodiversity," says Bob Pressey, a conservation planner in New South Wales, Australia, who has used such simulations to help with his own work.

In the meantime, Orme plans to do similar hotspot-mapping studies for other animal groups, such as mammals and amphibians. "We chose birds to start with because they are comparatively well understood," he says.